More than ten million people in the United States of America suffer from diabetes, a deficiency in the ability to regulate blood glucose levels. Individuals afflicted with the disease must control their blood glucose levels by measuring their blood glucose levels as frequently as possible and adjusting their food intake, level of physical activity and insulin dosage to regulate the glucose level. Blood glucose level is measured using one of several available invasive techniques.
Invasive techniques require a blood sample from the patient each time an analysis is to be performed. An accurate laboratory blood analysis requires about 5 to 10 ml of blood, and analysis using a laboratory instrument designed for performing such a biochemical analysis. However, the results of the test often are not available for several hours, and sometimes days. In addition, the instruments necessary to perform such an analysis are expensive and require that the blood samples be taken and analyzed by trained technicians.
Another invasive technique, referred to as a "finger stick" uses an integrated, self-contained instrument that evaluates a much smaller blood sample (approximately 0.25 ml). The small blood sample is obtained by puncturing a finger with a small lancet. The sample is then placed on a chemically treated carrier and inserted into the instrument. The finger stick devices normally provide the glucose concentration results in a few moments. However, they are still costly, and require that patient puncture a finger several times per day.
More recently, portable finger stick instruments have become available which require the use of single use, disposable, chemically treated carrier "strips". Although the portable instruments have a relatively low cost (about $100 to $300), the cumulative cost to diabetics for the normal supply of disposable carrier strips is considerable.
Invasive techniques for glucose analysis are problematic and suffer from poor compliance. Although diabetics can forestall the debilitating and often fatal complications of diabetes by frequent monitoring and control, only a small fraction of diabetics monitor their glucose levels as regularly as recommended. Diabetics find the current invasive methods of blood glucose monitoring painful, inconvenient and costly. To encourage frequent monitoring and control there is a clear need for a glucose monitor that requires no blood samples, is easy and convenient to use, is portable, and costs less than current methods.
Non-invasive methods for measuring blood glucose have been described. These methods include measurement of the optical polarization of light in the eye; the absorption, transmission, or scatter of infrared light in body tissue; or the chemical analysis of interstitial fluid removed through the skin by reverse iontophoresis (see, e.g., Rosenthal et al., U.S. Pat. Nos. 5,086,229; 5,279,543; Cote et al., IEEE Trans. of Biomed. Engineer. (1992) 39:752-56). However, to date none of these techniques has resulted in a commercially useful instrument. All of these methods have serious technical problems due to the small signals available and the inherent variability of measurements in live tissue. Furthermore, due to the complexity of the implementation, these methods are not likely to lead to small, low-cost instruments that will encourage frequent testing by diabetics.